Set default activity filter for BuddyPress (legacy or nouveau template pack)

bp-custom.php

<?php
/**
 * Custom functions
 */

// Exit if accessed directly
defined( 'ABSPATH' ) || exit;

function set_default_activity_filter() {
	$handle   = 'bp-nouveau';
	$position = 'before';

	if ( 'nouveau' !== bp_get_theme_package_id() ) {
		$handle = 'bp-jquery-cookie';
		$position = 'after';
	}

	wp_add_inline_script( $handle, sprintf( '
		( function( $ ) {
			// Replace with the activity type of your choice.
			var defaultActivityType = \'new_member\';

			if ( \'bp-nouveau\' === \'%s\' ) {
				var activityVars = sessionStorage.getItem( \'bp-activity\' ), store;

				if ( activityVars ) {
					store = JSON.parse( activityVars );

					if ( ! store.filter || \'0\' === store.filter ) {
						store.filter = defaultActivityType;
						sessionStorage.setItem( \'bp-activity\', JSON.stringify( store ) );
					}
				}
			} else if ( \'undefined\' !== typeof $.cookie ) {
				if ( \'-1\' === $.cookie( \'bp-activity-filter\' ) || ! $.cookie( \'bp-activity-filter\' ) ) {
					$.cookie( \'bp-activity-filter\', defaultActivityType, {
						path: \'/\',
						secure: ( \'https:\' === window.location.protocol )
					} );
				}
			}

		} )( jQuery );
	', $handle ), $position );
}
add_action( 'bp_enqueue_scripts', 'set_default_activity_filter', 20 );